The present invention relates to apparatus for signal processing systems and, more particularly, to apparatus for correcting errors introduced by the recording and reproduction of color video signals.
In the NTSC format for broadcast television signals, the chrominance information of a color video signal is carried by a pair of quadrature signal components which are phase and amplitude modulated upon a color subcarrier; e.g., 3.58 MHz, in U.S. standards. The color subcarrier is phase modulated by the color hue information and amplitude modulated by the color saturation information.
When the composite video signal is recorded on a record medium, for example, magnetic tape, the subsequent playback of the record medium introduces timing errors in the phasing of the color subcarrier. These timing errors may be attributed to flutter and wow in the magnetic recording and reproduction as well as mechanical difficulties such as non-uniform tape motion, tape stretch, and changes in tape tension.
Heretofore, a number of color correction schemes have been employed to overcome the difficulty of reproduction of color signals. Among these methods are the use of variable delay lines, prerecorded pilot tones and relatively complex servo control systems for tape speed and tension. These correction arrangements, however, are generally limited to recorder-reproducing systems having small inherent, absolute timing errors as illustrated by the professional quality studio-type recorder-reproducers. These correction circuits are both expensive and highly complex which generally prohibits their use in recorder-reproducer systems designed for consumer, educational, and industrial uses.